Disable prebuilts when building with clang coverage

Prebuilts broke the cf_x86_phone-userdebug_coverage_bionic
on tm-release build.

Bug: 230478310
Bug: 223592962
Test: presubmit
Merged-In: I3ed091156c4b39dad6eaf578144ac3d070025988
Merged-In: I9731400acfade95b3eab8f2d99fddb4cf856aa91
Merged-In: I6eca2fcc670dccef4a6cd9dc3f08003eb47e5bca
Change-Id: I40c10e88b824e5f4b783b1dc0a500096fad209b2